# Planarization of Substrate Topography by Spin Coating

Planarization of Substrate Topography by Spin Coating

Authors: L. E. Stillwagon, R. G. Larson, and G. N. Taylor

J. Electrochem. Soc. 134, 8, 2030-2037

## Contents

#### Soft matter keywords

Spin coating, thin films, capillarity, viscosity

By Alex Epstein

### Abstract from the original paper

The results of a study of topographic substrate planarization with films applied by a spin-coating process are reported. It is shown that spin coating produces conformal film profiles over topographic gaps on the substrate that are wider than about 50 um and that leveling of these gaps can only occur after spinning ceases if the film is able to flow over large distances. A comparison of the major forces acting on the film leads to the conclusion that the flow is driven primarily by capillarity when the width of the gap is less than 5000 um. A theory is developed that relates the time required to level the gaps to their width and to the thickness and viscosity of the film. The results of experiments performed to test the theory are presented and discussed.

## Soft matters

### Brief background

Spin coating is a widely used technique for coating a flat substrate with a thin film of a liquid material. It is particularly used in the electronics industry, where integrated circuits are manufactured by a sequence of photolithographic steps. However, these processing steps often result in not-so-flat topography. Modern IC's feature multi-level interconnects that can extend microns upward. Consider that the empirical "Moore's Law" tells us that maximum transistor density has been doubling in new computing hardware every 18 months. Now consider basic physics as it applies to photolithography: resolution or minimum linewidth (l) and depth of focus (d) are related to the exposure wavelength ($\lambda$) and the numerical aperture (NA) of the lens as follows.

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